Petrified Forest, Arizona (March 2010)

Located in the northeastern part of Arizona. The national park is filled with petrified logs. According to the guide "this high, dry grassland was once a vast floodplain crossed by many streams ... The trees fell and swollen streams washed them into adjacent floodplains. A mix of silt, mud, and volcanic ash buried the logs. This sediment cut off oxygen and slowed the logs' decay. Silica-laden groundwater seeped through the logs and replaced the original wood tissues with silica deposits. Eventually the silica crystallized into quartz, and the logs were preserved as petrified wood."